Making artificial stone from magnesite.



forms which may be made.

MIKLOS GERSTER, OE BUDAPEST, AUSTRIA-HUNGARY, ASSIGNOR OF ONE-HALF TO HEINRICH FREUND & SDHNE, OF

TRIA-HUNGARY.

BUDAPEST, AUS- IVIAKING ARTIFICIAL STONE FROM MAGNESITE.

Specification of Letters Patent.

Patented Oct. 31, 1905.

Application filed February 3, 1905. Serial No. 244,044.

To all whom it nan/y concern:

Be it known that I, MmLos GERsTER, a subject of the Emperor of Austria-Hungary, residing at Budapest, Austria-Hungary, have invented certain new and useful Improvements in Making Artificial Stone from Magnesite, of which the following is a specification.

Artificial stone or bricks ofmagn esite have formerly been madeby subjecting the magnesite to long-continued burning at a very high temperature, after Which it is coarsely granulated, pressed into suitable form, and

then again burned. Various forms are made for various purposes, and I use the term brick in its generic sense to cover all the In order that the bricks made in this way should not become deformed during the hardening consequent upon the second burning, the first burning of the non-granulated or raw magnesite has generally been continued until the magnesite has lost from thirty to fifty per cent. of its original volume. The magnesite thus considerabl y reduced in volume (and consequently very slightly or not at all reduced in the second burning) has been so far granulated that the particles or granules have a cross-section of about one millimeter. This granulated product has been then pressed into brick-form and burned a second time. The process becomes very costly and tedious on account of the first burning of the raw material to effect a shrinkage of thirty to fifty per cent, be

cause, on the one hand, the long-continued burning is a matter of much expense, and, on the other hand, the so fully burned magnesite is extremely hard and very difiicult to granulate. The accompanying invention aims to avoid these disadvantages, and it may be'generally stated that according to this invention the shrinking or reduction of the magnesite to the desired extentin the preparatory stages of the process is divided into two very distinct phases. The first phase is of a chemical nature and continues until the carbonic-acid gas in the magnesite has been driven offwhile the second phase begins from this point and is of a physical nature. In the first stage only is the hardening or shrinking necessarily accomplished by heat. In the second stage the shrinking is accomplished without the employment of any heat, but entirely by mechanical means. For example, the complete process may be carried out as follows: The magnesite in its first burning is not brought down to thirty to fifty per cent, as formerly, but preferably is only so far burned as to drive out the cagbor ic acid. During this burning, the period of which obviously need not be calculated with absolute exactness, the magnesite loses at most twenty per cent. of its volume, but usually only ten per cent. The further diminution in volume by mechanical methods is preferably obtained by granulating the entire mass of burned magnesite to such a degree of fineness that its porosity is substantially diminished. The diminution of the porosity is preferably such that the volume of pores or cells in the green-pressed brick (pressed with substantially the same or higher pressure as in the previous processes) bears the same relation to the total mass as in green bricks made according to the old process. Thus the fine granulation will have partly taken the place in efi'ecting a shrinking of the material of the long-continued burning of the old process. Investigations have shown that the magnesite burned until the carbonic acid is driven off may advantageously be granulated in order to obtain the desired effect to such a fineness as to pass through a sieve of about one-third to two-thirds of a millimeter cross-section. Thus the operator has a determined and observable range of fineness of granulation which corresponds to the quality of the burned material.

An important advantage of the invention is that the magnesite burned free of carbonic acid, as described above, is so much softer than the magnesite burned to a reduction of thirty to fifty per cent. under the old process that the especially fine granulation above mentioned may be accomplished much more easily and with less cost than the coarse granulation carried on under the previous processes. The complete hardening of the brick may then be secured by a second burning in the ordinary Way.

The surface of the bricks made in this Way is very smooth and the bricks have sharp corners, so that in use they require very little binding material.

The shrinkage in volume above referred to must be distinguished from the shrinkage in mass or Weight. The loss of Weight of the raw magnesite will be obviously the same whether it be burned until it is completely hardened or only until all the carbonic acid is driven off, since the maximum loss of weight is identical with the quantity of carbonic acid originally contained in the magnesite. On the other hand, the loss of volume depends on the physical structure, the amorphous structure of the magnesite which exists at first after the driving off of the carbonic acid being gradually changed by long heating at a high temperature to a crystalline structure, and this change is accompanied by a reduction in volume. It is this reduction in volume which, according to the present invention, is brought about not by the action of heat but by mechanical means.

Though I have described with great particularity of detail a specific process embodying my invention, yet it is not to be understood therefrom that the invention is limited to the exact process described. Various modifications may be made by those skilled in the art without departure from the invention.

What I claim is l. The process of making bricks from magnesite which consists in burning the raw material only to such a point as to accomplish a part of the reduction in volume necessary before the second burning, granulating the burned magnesite so finely as to accomplish a substantial part of such reduction in volume, whereby the cost of burning is lessened and the granulation is facilitated, pressing the granulated material into bricks and burning such bricks.

2. In the manufacture of bricks from magnesite, the method of preparing the magnesite which consists in burning it to produce a reduction of less than thirty per cent. in volume, and granulating this burned product to such a fineness as to avoid substantial deformation in the final burning.

3. In the manufacture of bricks from magnesite, the process of preparing the magnesite which consists in burning the magnesite only to the point at which the carbonic acid is driven off therefrom, and then granulating the burned material to such a pointas will avoid substantial deformation in the final burning.

In witness whereof I have hereunto signed my name in the presence of two subscribing witnesses.

MIKLOS GERSTER.

Witnesses:

FRANK E. MALLETT, CHARLES E. BALTZo. 

